Not Applicable.
This invention relates in general to leveling sheet metal by stretching it and more particularly to a clamping assembly and process for gripping the sheet metal without leaving perceptible indentations or otherwise marring it.
Steel sheet finds widespread use in manufactured products of many varieties. In some, such as housings, cabinets and covers of one type or another, relatively large expanses of sheet metal are exposed and are highly visible. But steel sheet as it is sold by steel mills contains imperfections, such as warpage and wavy regions, that render it unsuitable for such products. The steel needs further processing, and that processing takes the form of leveling, that is, stretching the metal sheet slightly beyond its yield point to give it a more uniform surface appearance.
One type of leveling machine has rolls arranged in two sets, one set beyond the other. The strip of steel sheet passes through the two sets of rolls, both of which are arranged to grip it firmly. The downstream set rotates faster than the upstream set, and the steel sheet undergoes a measure of stretching in between the two sets of rolls. But these machines subject the strip to substantial distortions as the strip passes over the rolls, and further require enormous power.
Another type of leveling machine grips the sheet with two sets of jaws which are spaced apart. Once the jaws of the two sets clamp down on the sheet, the two sets are forced apart, thereby stretching and leveling the sheet metal. The jaws enable this type of machine to grip the sheet metal along reasonably large surface areas, and slippage for all intents-and-purposes is eliminated.
However, care must be exercised to insure that the jaws, in the process of eliminating warpage, do not themselves create surface markings or other imperfections. In this regard, the jaws used on leveling machines clamp down with considerable force on the sheet metal and may leave indentations at the sides of the jaws. The problem is particularly acute with stainless steel sheet, because it is more reflective than low carbon steel and less likely to be painted. As a consequence, surface markings and other imperfections in stainless steel sheet are more perceptible.
The present invention resides in two opposing jaws which have the capacity to clamp down on and grip sheet metal in a leveling machine without marring the surface of the sheet metal. The jaws concentrate the clamping force away from the side edges of the area that is gripped, so that the jaws are less likely to leave perceptible marks on the sheet metal. To this end, a traditional flat gripping pad is installed in one of a pair of jaws, and it is backed by a shim which is narrower than the surface which backs it, thus enabling the pad to flex and assume a slightly bowed configuration under the force applied to it, and in this configuration the actual gripping surface on the pad is slightly convex. The invention also resides the process of installing a shim behind one of the pads to concentrate the gripping force along the center of the pad. The invention also consists in the parts and in the arrangements and combinations of parts hereinafter described and claimed.